1. Field of the Invention
The present invention is directed to an improved plasma processing system, and particularly to a plasma processing system in which all surfaces of the system can be biased electrically and/or can be heated or cooled to improve the overall cleanliness of the system. The present invention can also control the wall coatings to be the proper amount to positively effect the process. The present invention also is directed to the process of cleaning such a processing system.
2. Description of the Background
High-density plasma processing systems are used for plasma etching and/or depositing thin films. Different parts of the plasma sources of the system are coated with condensable species generated during the plasma etching and deposition processes. The species deposited on various surfaces of the source affect the gas chemistry of the plasma source in various ways. For example, some deposits getter (i.e., remove from a gas) reactive species from the plasma, thus lowering etching and deposition rates. Other species on source surfaces, while they are condensable, also have high-enough vapor pressures that they can be desorbed from source surfaces, thereby changing the gas composition of the plasma. Gas species that adsorb on the wall are often radicals and polymerize with existing wall coatings to create species with must different vapor pressure and/or reactivity. Gas species that are condensed on the walls can also be crosslinked by electrons, ions or photon fluxes from the plasma to generate much different vapor pressure and/or reactivity species. Changes in the gas composition of the plasma by gettering, desorption of condensed species. or any other means, particularly in unregulated ways, results in loss of control of the of the total process. Herein, changes in the gas composition by any of these processes will be described generally as changes due to xe2x80x9cwall contributions to process gas.xe2x80x9d
Particle contamination has become an ever increasing problem as the complexity of integrated circuits increases and the feature size of these circuits decreases. Although clean-rooms had already greatly reduced contamination due to the ambient atmosphere by 1990, it was generally recognized by that time that processing tools and the processes themselves were major contributors of particle contamination. See Selwyn et al., Appl. Phys. Lett, 57 (18) 1876-8 (1990). Plasma processors had already been identified as major sources of contamination. See Selwyn et al., J. Vac. Sci. and Technol. A, 7 (4) 2758-65 (1989); Selwyn et al., 1990; Selwyn et al., J. Vac. Sci. and Technol. A, 9 (5) 2817-24 (1991(a)); and Selwyn, J. Vac. Sci. and Technol. A, 9 (6) 3487-92 (1991(b)). By 1990, suspended particles had been observed at the plasma/sheath boundary in plasmas used to etch, (see Selwyn et al., 1989), deposit (see Spears et al., IEEE Trans. Plasma Science, PS-14 (2) 179-87 (1986)) and sputter (see Jellum et al., J. Appl. Phys., 67 (10) 6490-6 (1990(a))). These suspended particles become negatively charged (see Wu, et al., J. Appl. Phys., 67 (2) 1051-4 (1990) and Nowlin, J. Vac. Sci. and Technol. A, 9 (5) 2825-33 (1991)) in the plasma and become trapped at the plasma/sheath boundary (Selwyn et al., 1990 and Carlile, Appl. Phys. Lett., 59 (10) 1167-9 (1991)).
When the plasma is extinguished, the particles may fall onto the wafer surface, thereby contaminating it. By 1992, it was believed that 70% to 80% of total wafer contamination was contributed by tools and processes used in device fabrication, and plasma processors are among the xe2x80x9cdirtiestxe2x80x9d tools in modern fab lines. See Selwyn, J. Vac. Sci. and Technol. A, 10 (4) 1053-9 (1992).
Consequently, much attention has been directed to controlling particle generation in plasma processors and the cleaning of such reactors. However, the influence of process parameters and chamber design on both the reduction of wall deposits and in-situ reactor cleaning has been considered (see Vogt et al., Surface and Coatings Technol., 59 (1-3) 306-9 (1993)); and the control of particulate contamination by means of a self-cleaning tool design has been described (see Selwyn et al., 1992). The optimization of in-situ cleaning procedures using fluorinated reactive gases has recently been considered. See Sobelewski et al., J. Vac. Sci. and Technol. B, 16 (1) 173-82 (1998); Ino et al., Japanese J. Appl. Phys. 33 Pt. 1 (1B) 505-9 (1994) and Ino et al., IEEE Trans. on Semicon. Mfg., 9 (2) 230-40 (1996).
Yoneda (U.S. Pat. No. 4,430,547) describes an in-situ self-cleaning parallel plate plasma apparatus in which electrodes are heated by means of embedded resistive heaters or a circulating heated fluid. Benzing (U.S. Pat. No. 4,657,616) and Krucowski (U.S. Pat. No. 4,786,392) describe an inconvenient set of removable fixtures which must be placed inside the process chamber when cleaning becomes necessary and removed when cleaning has been completed. Benzing (U.S. Pat. No. 4,786,352) includes two or more electrodes on the exterior surface of a dielectric processor chamber, and, by applying an RF voltage between the two or more electrodes, establishes a plasma within the chamber for in-situ cleaning. Hayes (U.S. Pat. No. 4,795,880) uses the heating coil of a tube furnace as the inductive heating element by which a cleaning plasma is established within the tube. The cleaning is accomplished at furnace operating temperatures. Law (U.S. Pat. No. 4,960,488) describes a single-wafer processing chamber with the capability of a localized chamber self-etch and a wide area chamber self-etch. Both etches are possible due to the wide range of pressures at which the chamber may be operated and the variable electrode spacing. Aoi (U.S. Pat. No. 5,084,125) describes a processing chamber that has a processing section and a cleaning section. A movable wall is positioned alternately in the processing section and in the cleaning section. Neither chamber disassembly nor process interruption for cleaning is necessary. Moslehi (U.S. Pat. Nos. 5,252,178 and 5,464,499) describes a multi-zone and multielectrode plasma processing system. The apparatus permits activation of the multiple plasma electrodes in either a continuous or multiplexed format. Process gas flows may be stopped intermittently and a cleaning gas introduced so that an in-situ cleaning process occurs. Sekiya (U.S. Pat. No. 5,269,881) covers the interior surfaces of a parallel plate processing chamber with multiple conducting electrodes which are insulated from each other. A high frequency electric field is applied sequentially between the electrodes in various electrical configurations to achieve in-situ cleaning. Blalock (U.S. Pat. Nos. 5,514,246 and 5,647,913) describes an inductively coupled plasma reactor that includes a capacitive coupling electrode located between the exterior surface of the chamber wall and the induction coil used to excite the plasma. An RF field established between the capacitive coupling electrode and conductors within the chamber produces a cleaning plasma. Sandhu (U.S. Pat. Nos. 5,523,261 and 5,599,396) describes an inductively coupled plasma reactor in which a capacitive coupling electrode is used to facilitate cleaning as in Blalock. However, in contrast to Blalock, the electrode comprises a conducting liquid or a conducting polymer that fills a void between the inner and outer wall of the process chamber and is active only during chamber cleaning.
Grewal (U.S. Pat. Nos. 5,597,438) describes an etch chamber with three independently controlled electrodes. Both inductive and capacitive coupling are used. Usami (UK Patent Application No. 2,308,231) describes a capacitively excited reactor in which the counter electrode is not planar. It may be cleaned by exciting a cleaning plasma with the sample holder being either the powered or grounded electrode. In one embodiment, power at two frequencies is used during the cleaning procedure.
During plasma etching, etch rates vary in uncontrolled ways and a uniformity of etching can be greatly reduced in the presence of wall contribution to process gas. During plasma deposition, deposition rates, the composition of the deposited films, and the uniformity of film deposition are all affected in non-uniform and uncontrolled ways by wall contribution to process gas. Consequently, since the chemistry at surfaces in these sources was not controllable previously, the overall processes being implemented using the sources previously was uncontrolled. These changes in the wall contribution to process gas can change during the processing of a single wafer or over a longer time such generating changes from wafer to wafer.
Heating of the walls of deposition and etch process chambers during etching or deposition to minimize condensation is known. In deposition reactors heating surfaces hot enough to cause chemical reactions enhances the deposition rate of the material that one wishes to deposit, but heating to a temperature short of the chemical reaction threshold promotes desorption of effluents. However, heating all surfaces of a reactor while simultaneously bombarding them with plasma species form volatile compounds of the undesired wall absorbed species has not to our knowledge previously been described. Furthermore, it has not heretofore been possible in reactors that differ from the ESRF source.
Applied Materials, of Santa Clara, Calif. sells an etching reactor that uses fluorine chemistry and employs a heated silicon top plate to convert fluorine radicals (F*) to molecular fluorine (F2) during the etching reactions, but not during cleaning of the reactor. Some other known systems have tried to control chemical changes on individual surfaces during processing, such as is disclosed in Japanese application 61-289634 entitled xe2x80x9cDry etching,xe2x80x9d in which a polymer is prevented from being formed on an electrode by attaching alumina rings to an outer surface of the electrode; Japanese application 62-324404 entitled xe2x80x9cEtching Device,xe2x80x9d in which a hot water-based heater is attached to a silica chamber to improve etching performance; and Japanese application 63-165812 entitled xe2x80x9cEtching Device,xe2x80x9d in which an electrical heater is attached to a chamber to prevent reaction products from sticking to the surface. The contents of each of these applications is incorporated herein by reference. However, if only selected surfaces have controlled chemistries, then the remaining surfaces which are less reliably controlled control the overall introduction of wall contribution to process gas into their corresponding systems.
Still another problem with known systems is slow cleaning of surfaces within sources using plasma etching. In fact in many reactors the cleaning time significantly exceeds the process time, especially for thickly deposited materials. Such reactors are inherently very cost-ineffective.
Some known systems have utilized electrical biasing of individual components during cleaning, such as is disclosed in U.S. Pat. No. 5,269,881 to Sekiya et al., entitled xe2x80x9cPlasma Processing Apparatus and Plasma Cleaning Methodxe2x80x9d, in which a high voltage is applied individually to each of three electrically isolated conductive blocks during cleaning; Japanese application 57-42131 entitled xe2x80x9cParallel Flat Board Type Dry Etching Device,xe2x80x9d in which the polarity of an electrode is reversed between sputtering and cleaning; Japanese application 60-59739 entitled xe2x80x9cDry Cleaning Method,xe2x80x9d in which a high frequency power is applied between a substrate electrode and a cleaning electrode to remove a silicon film; and
Japanese application 61-10239, entitled xe2x80x9cSemiconductor Manufacturing Equipment,xe2x80x9d in which the grounding self-bias of an anode plate is eliminated during a plasma etching/cleaning process. The contents of each of these applications is incorporated herein by reference. However, as described above in terms of controlling chemistry on surfaces, if only selected surfaces are cleaned, then the remaining surfaces which are less reliably cleaned control the overall uncleanliness of their corresponding systems.
It is a first object of the present invention to address at least one disadvantage of known plasma processing systems.
It is a second object of the present invention to provide a method for controlling the chemistry at all surfaces of a high-density plasma source.
It is a third object of the present invention to provide an improved method of cleaning a plasma processing system which reduces cleaning time of the plasma sources.
These objects and other objects of the invention are achieved by providing the capability to both regulate a temperature of and to electrically bias, each of the surfaces in the source. This regulation is enabled by using materials for all surfaces in the source which assist in controlling the chemical reactions that occur at each surface.